Liquid treatment system for high ph water

ABSTRACT

A packing composition effective to reduce the pH of alkaline liquids, used as a pretreatment, in association with a reverse osmosis membrane and support in a liquid treatment system, is made of an encapsulating matrix of polymeric material that is essentially water impermeable at a pH between about 4.5 and 8 and which becomes significantly water permeable at a pH above about 9, and an acidulous material which is encapsulated by the matrix at a pH between about 4.5 and 8, and released progressively from the matrix at a pH above about 9.

United States Patent Chamberlin et al.

[ 51 June 5, 1973 [56] References Cited UNITED STATES PATENTS 2,528,84711/1950 Van Norden ..2l0/5 0l 2,955,067 10/1960 McBumey et al ..210/505Primary Examiner-Frank A. Spear, Jr, 7 Attorney-- F S hapoe and AlexMich, Jr.

[57] ABSTRACT A packing composition effective to reduce the pH ofalkaline liquids, used as a pretreatment, in association with a reverseosmosis membrane and support in a liquid treatment system, is made of anencapsulating matrix of polymeric material that is essentially waterimpermeable at a pH between about 4.5 and 8 and which becomessignificantly water permeable at a pH above about 9, and an acidulousmaterial which is encapsulated by the matrix at a pH between about 4.5and 8, and released progressively from the matrix at a pH above about 9.

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REVERSE OSMOSIS PURIFICATION SYSTEM PURIFIED LIQUID LIQUID TREATMENTSYSTEM FOR HIGH pH WATER This is a division of application Serial No.058,788 filed July 28, 1970, now US. Pat. No. 3,684.094.

BACKGROUND OF THE INVENTION Cellulose acetate semipermeable membranesare well known for use in high pressure reverse osmosis fluidpurification systems. In present systems, however, the feed water pHmust be maintained between about pH 2.5 and pH 9.0. Feed waters outsidethis pH range will cause degradation of the cellulose acetate reverseosmosis membranes by hydrolysis and failure of the reverse osmosis fluidpurification system.

SUMMARY OF THE INVENTION We have found that pretreating high pH feedwater, in a liquid treatment system also containing a reverse osmosismembrane, by first passing the feed through a packing compositioncontaining about 1 to 60 weight percent of an acidulous materialdistributed through a high pH degradable polymeric materialencapsulating matrix that becomes water permeable at a pH above about 9,allowing significant contact of water with the acidulous material,reduced reverse osmosis membrane deterioration problems.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention, reference may be made to the preferred embodiment, exemplaryof the invention, shown in the accompanying drawing. This drawing showsa cross sectional illustration of a liquid treatment system comprising anew and improved liquid pretreatment system, containing the packingcomposition of this invention, and a reverse osmosis liquid purificationsystem containing a supported semipermeable membrane, with associatedmeans for introducing liquid feed into the pretreatment system, out ofthe system and into the reverse osmosis system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, aliquid treatment system is shown. One embodiment of a new and improvedhigh pH liquid pretreatment system is shown as 10. The pretreatmentsystem consists of a container 11, which may be metal, plastic, glass,or other suitable material, with associated liquid feed inlet means 12,outlet means 13 leading to a reverse osmosis purification system, and apretreatment packing composition 14 held within the container by porousretainer 15. The system can be used to pretreat liquids in associationwith a reverse osmosis liquid purification system 16, comprising asemipermeable reverse osmosis membrane 17 of either a cellulose ester orcellulose ether derivative, such as for example cellulose acetate,cellulose acetate butyrate,

cellulose proprionate or ethyl cellulose, and a porous support 18 forthe membrane. The membrane and support allow effusion of purified waterinto a suitable collecting means 19. The unpurified feed then passes outof the reverse osmosis system by means of outlet 20. The reverse osmosismembrane suitable for use in this system are well known and referencemay be made to US. Pat. No. 3,133,132 and 3,344,214 for details on theircomposition and manufacture. The support may be of fibrous filamentwound fiberglass having pores therethrough, a plastic or steel tubehaving holes therethrough or any other suitable porous support.Generally the membrane will be tubular and fit within the walls of thesupport.

The packing composition 14 comprises an acidulous material uniformlydistributed throughout the encapsulating matrix of a high pH degradablepolymeric material that is essentially water impermeable at atmosphericpressure. The packing composition must provide ease of flow for thefeed, have a large surface area in relation to its weight, provide aconsistent concentration gradient of acidulous material and allowprogressive release of the acidulous material in high pH liquids. It ispreferably employed inthe form of long thin fibrous strings or filamentsor small drops, beads or granules.

Examples of suitable acidulous materials would include acidulous salts(i.e. a salt that has an acid reaction to litmus or similar indicatorsin water) such as, for example, magnesium nitrate, magnesium chloride,magnesium sulfate, ammonium nitrate, ammonium chloride, ammoniumsulfate, silver nitrate, silver chloride, silver sulfate, lead nitrate,lead chloride, lead sulfate, iron nitrate, iron chloride, iron sulfate,aluminum nitrate, aluminum chloride, aluminum sulfate, and preferablyalumina in its variety of forms A1 0,; Al- O -H O, Al O -2H O; AI O -3HO).

These acidulous materials are uniformly distributed through andcontinuously encapsulated within the matrix of the polymeric chains of ahigh pH degradable polymeric encapsulating material which forms the mainstructure of the pretreatment packing composition. By high pH degradablepolymeric encapsulating material is meant any polymeric material that isessentially water impermeable or water insoluble, and essentially inertat a pH of between about 4.5 and 8, but degrades and/or dissolves at asignificant rate, and becomes significantly water permeable, generallythrough a hydrolysis reaction, at a pH of greater than about 9. Thisallows release of the contained acidulous salt and contact of water andthe acidulous salt by diffusion at a high pH. The encapsulating materialis not one hundred percent water impermeable at a pH of between about4.5 and 8 but would not allow significant diffusion of acid out of thematrix or significant diffusion of water into the matrix at atmosphericpressure until a pH of about 9 is reached, at which point there would bebulk diffusion of water and acid. The expression pH is employed as anindex of acid intensity (an acid solution having a pH less than 7 and abasic solution having a pH greater than 7), and pH being equal to thelogarithm of the reciprocal of the hydrogen ion concentration; i.e., pHlog l/[H per liter.

Examples of suitable polymeric encapsulating materials essentiallyimpermeable in water at a pH between about 4.5 and 8 but degradableabove a pH of about 9 include cellulose compounds containing chemicalgroups which are appreciably hydrolyzable in water at a pH of greaterthan about 9, such as cellulose acetate, cellulose propionate, cellulosebutyrate, cellulose acetate-butyrate, cellulose acetate-propionate,methyl cellulose and ethyl cellulose.

When cellulose acetate-alumina is used as the packing composition forthe pretreatment of high pH water, the essentially water insoluble andwater impermeable cellulose acetate polymeric matrix undergoeshydrolysis in a base environment (cellulose acetate OH cellulose OHacetate). The OH from the high pH water significantly degrades anddissolves the cellulose acetate. The alumina heretofore essentiallyunreacted and trapped along with bound water molecules in the celluloseacetate matrix is freed as the cellulose acetate is hydrolyzed tocellulose. Water is then highly absorbed into the degraded matrix andcontacts the freed alumina (which undergoes the reaction A1 H O 2H* 2AlOproducing bulk diffusion of an acid (H*), to partially neutralize thehigh pH feed. The higher the pH of the feed the faster the acid will bereleased from the encapsulating matrix.

In one method, the packing is made by casting a continuous fibrousfilament from a casting solution comprising the cellulose compound, theacidulous salt, a leachable organic pore producing swelling agent suchas triethyl phosphate, tetrahydrofurfuryl phosphate or a substantiallywater soluble liquid amide such as formamide (HCoNH dimethyl formamide,methyl formamide or ethyl formamide, and a leachable organic solventsuch as acetone, methyl ethyl ketone, ethyl alcohol or methyl alcohol.The casting solution is poured of the salt throughout the packing whenit is placed in the pretreatment system.

The composition of matter constituting the packing could be made byother suitable techniques such as hot melt extrusion of the polymericmaterial and salt through a shaped opening to give the desired crosssection. It could also be cast in flat, thin membrane form by standardcasting and leaching techniques.

The acidulous material is generally added to the polymeric encapsulatingmaterial in particulate form. The acidulous material particle size canrange up to about 297 microns diameter (No. 50 mesh U.S. Sieve Seriesdesignation). The preferred particle size range is from about 0.002micron to 1 micron diameter. The acidulous material must constitutebetween about 1 to 60 weight percent of the dry packing, based on theweight of acidulous material plus high pH degradable polymericencapsulating material, with a preferred range between about to 45weight percent acidulous material. Below 1 weight percent, the pH willnot be effectively reduced. Above 60 weight percent, acidulous material,the pretreatment packing will tend to crumble.

EXAMPLE 1 A casting solution was prepared containing 16 ounces ofcellulose acetate, 6 ounces of alumina having an average particle sizeof 0.03 microns, 47 ounces of acetone and 31 ounces of formamide.

The solution was ball milled for three hours and cast into a continuous,fibrous packing filament by slowly pouring the casting solution into astream of cold water. This procedure provided a short air contact timefor the casting solution and resulted in the water stream shearing thestream of casting solution, congealing it to a more viscous form andleaching out the acetone and forrnamide at the same time, to provide avery thin packing filament that was caught on a sieve.

The packing had a large surface area to weight ratio, a celluloseacetate polymeric matrix encapsulating the interdispersed aluminaacidulous material, and a thin cellulose acetate skin'that was verydense as compared to the rest of the structure. These packing fiberswere from about 10 to 40 mils (0.01 0.04 inch) in diameter.

A two foot long 1% inch LD. steel pipe was packed with 3 ounces of thedried cellulose acetate-alumina packing filament and capped at both endsexcept for an inlet and outlet tube, to form a pretreatment system.Water containing about 200 ppm impurities was fed through the pipecontaining the pretreatment packing composition at a rate of 30milliliters per minute. The pH of the water entering and leaving thepretreatment system was measured for a variety of feed pHs. The resultsare shown in Table 1.

TABLE 1 pH of Water Going Into pH of Water Coming Out PretreatmentSystem of Pretreatment System The pretreatment system lowered the pH ofthe feed water to a safe level (pH below 9) at the high pH but did notlower it to the acid region (pH below about 4.5 will also start to causemembrane deterioration) for the lower pH feed.

As can be seen the packing is self-metering and progressively releasesacid. At an initial pH of 10.7 the reduction was 2 pH units, whereas atan initial pH of 8.1 the reduction was only 0.4 pH units, due to thefact that the polymeric encapsulant will not degrade as fast at lower pHvalues and less acidulous salt will be freed to effect neutralization.Other advantages of the pretreatment system are its low cost and ease ofinsertion into or removal from a liquid treatment system.

This pretreatment system was also operated for four weeks in a fluidtreatment system also containing a supported cellulose acetate reverseosmosis membrane in a home water treatment module. The module producedabout 2.2 gallons per day drinking water from a 10 gallon per day feedcontaining about 200 ppm impurities. The pH of the feed going into thepretreatment system was 10 and the pH of the feed coming out of thepretreatment system and into the reverse osmosis fluid purificationsystem was 8.5 During thefour weeks of operation, the cellulose acetatereverse osmosis membrane in the module showed no sign of degradation dueto hydrolysis.

We claim as our invention:

1. A packing composition effective to reduce the pH of alkaline liquidscomprising an encapsulating matrix of polymeric material and anacidulous material distributed therethrough said matrix capable ofencapsulating theacidulous material at a pH between about 4.5 and 8 andprogressively releasing the acidulous material at a pH above about 9.

2. A packing composition effective to reduce the pH of alkaline liquidscomprising:

a. a matrix of polymeric material that is essentially water impermeableat a pH between about 4.5 and 8 and which becomes substantially waterpermeable at a pH above about 9, and

b. an acidulous material distributed throughout and encapsulated by thematrix.

3. The composition of claim 2 wherein the acidulous material isuniformly distributed throughout the matrix and constitutes from about 1to 60 weight percent of the packing composition.

4. The composition of claim 3 wherein the acidulous material is selectedfrom the group consisting of alumina, magnesium nitrate, magnesiumchloride, magnesium sulfate, ammonium nitrate, ammonium chloride,ammonium sulfate, silver nitrate, silver chloride, silver sulfate, leadnitrate, lead chloride, lead sulfate, iron nitrate, iron chloride, ironsulfate, aluminum nitrate, aluminum chloride and aluminum sulfate.

5. The composition of claim 3 wherein the polymeric materialconstituting the matrix comprises a cellulose compound containing achemical group which is appreciably hydrolyzable in water at a pHgreater than about 9 6. The composition of claim 5 wherein the polymericmaterial constituting the matrix is selected from the group consistingof cellulose acetate, cellulose propionate, cellulose butyrate,cellulose acetate-butyrate, cellulose acetate-propionate, methylcellulose and ethyl cellulose.

7. The composition of claim 5 wherein the acidulous 'material is aluminaand the polymeric material constimeable at a pH above about 9, and l to60 weight percent of a particulate acidulous material and (2) congealingsaid liquid admixture to form a polymeric matrix encapsulating saidacidulous material.

9. The method of claim 8 wherein the admixture is a hot liquid, said hotliquid being extruded through a shaped opening, and thereafter congealedby cooling.

10. The method of claim 8 wherein the admixture also contains aleachable solvent, a leachable swelling agent and the admixture iscongealed by leaching the admixture to form a matrix of polymericmaterial with acidulous material distributed throughout and encapsulatedby the matrix.

11. The method of claim 10 wherein the acidulous material is aluminahaving a particle size range from about 0.002 to 297 microns and thepolymeric material is selected from the group consisting of celluloseacetate, cellulose propionate, cellulose butyrate, celluloseacetate-butyrate, cellulose acetate-propionate, methyl cellulose andethyl cellulose.

2. A packing composition effective to reduce the pH of alkaline liquidscomprising: a. a matrix of polymeric material that is essentially waterimpermeable at a pH between about 4.5 and 8 and which becomessubstantially water permeable at a pH above about 9, and b. an acidulousmaterial distributed throughout and encapsulated by the matrix.
 3. Thecomposition of claim 2 wherein the acidulous material is uniformlydistributed throughout the matrix and constitutes from about 1 to 60weight percent of the packing composition.
 4. The composition of claim 3wherein the acidulous material is selected from the group consisting ofalumina, magnesium nitrate, magnesium chloride, magnesium sulfate,ammonium nitrate, ammonium chloride, ammonium sulfate, silver nitrate,silver chloride, silver sulfate, lead nitrate, lead chloride, leadsulfate, iron nitrate, iron chloride, iron sulfate, aluminum nitrate,aluminum chloride and aluminum sulfate.
 5. The composition of claim 3wherein the polymeric material constituting the matrix comprises acellulose compound containing a chemical group which is appreciablyhydrolyzable in water at a pH greater than about
 9. 6. The compositionof claim 5 wherein the polymeric material constituting the matrix isselected from the group consisting of cellulose acetate, cellulosepropionate, cellulose butyrate, cellulose acetate-butyrate, celluloseacetate-propionate, methyl cellulose and ethyl cellulose.
 7. Thecomposition of claim 5 wherein the acidulous material is alumina and thepolymeric material constituting the matrix is cellulose acetate.
 8. Amethod of making a packing composition useful in reducing the pH ofalkaline liquids comprising (1) admixing a liquid comprising a polymericmaterial that is essentially water impermeable at a pH between about 4.5and 8 and which becomes substantially water permeable at a pH aboveabout 9, and 1 to 60 weight percent of a particulate acidulous materialand (2) congealing said liquid admixture to form a polymeric matrixencapsulating said acidulous material.
 9. The method of claim 8 whereinthe admixture is a hot liquid, said hot liquid being extruded through ashaped opening, and thereafter congealed by cooling.
 10. The method ofclaim 8 wherein the admixture also contains a leachable solvent, aleachable swelling agent and the admixture is congealed by leaching theadmixture to form a matrix of polymeric material with acidulous materialdistributed throughout and encapsulated by the matrix.
 11. The method ofclaim 10 wherein the acidulous material is alumina having a particlesize range from about 0.002 to 297 microns and the polymeric material isselected from the group consisting of cellulose acetate, cellulosepropionate, cellulose butyrate, cellulose acetate-butyrate, celluloseacetate-propionate, methyl cellulose and ethyl cellulose.